RU2414070C2 - Method of compensating for internal delays within each node and transmission delays between nodes - Google Patents

Method of compensating for internal delays within each node and transmission delays between nodes Download PDF

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Publication number
RU2414070C2
RU2414070C2 RU2006114170/09A RU2006114170A RU2414070C2 RU 2414070 C2 RU2414070 C2 RU 2414070C2 RU 2006114170/09 A RU2006114170/09 A RU 2006114170/09A RU 2006114170 A RU2006114170 A RU 2006114170A RU 2414070 C2 RU2414070 C2 RU 2414070C2
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node
multiplexer
real
time clock
number
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RU2006114170/09A
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Russian (ru)
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RU2006114170A (en
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Геир Андре Мотцфельдт ДРАНГЕ (NO)
Геир Андре Мотцфельдт ДРАНГЕ
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Вестернджеко Сайзмик Холдингз Лимитед
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J3/00Time-division multiplex systems
    • H04J3/02Details
    • H04J3/06Synchronising arrangements
    • H04J3/0635Clock or time synchronisation in a network
    • H04J3/0638Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0647Synchronisation among TDM nodes
    • H04J3/065Synchronisation among TDM nodes using timestamps

Abstract

FIELD: information technology.
SUBSTANCE: method for compensating for one or more transmission delays between a multiplexer, a first node and a second node. In one version, the method includes synchronising a first real time clock of the multiplexer as the real time clock of the first node and as the real time clock of the second node; receiving data from the first node; calculating a transmission delay between the multiplexer and the first node using an equation (RTCK+DelayK)mod(M·Tslot)=(K−1)·Tslot, where M refers to the number of time slots within a bandwidth of a medium configured for communicating data between the multiplexer, the first node and the second node, Tslot refers to the duration of each time slot, K refers to a node address, mod refers to a modulo operation, RTCK refers to the real time clock of the Kth node and DelayK refers to accumulated transmission delay from the multiplexer to the Kth node; sending a second real time clock of the multiplexer, a first number and the transmission delay to the first node; and setting the real time clock of the first node to be equal to the second real time clock of the multiplexer plus the transmission delay.
EFFECT: higher accuracy of synchronising real time clocks.
29 cl, 4 dwg

Description

FIELD OF THE INVENTION

Various embodiments of the present invention are generally related to a network environment, and more specifically, to responding to delays within a network environment.

BACKGROUND

Time Division Multiplexing (TDM) is a technology for allocating bandwidth (link capacity) across multiple channels to allow bit streams to be combined (multiplexed). Bandwidth allocation is accomplished by dividing the time axis into time intervals of fixed duration. A particular channel, in this case, can transmit only during a separate time interval. A circuit that combines signals on the (transmitting) side of a communication source can be called a multiplexer. It receives input from each individual end user, splits each signal into segments, and distributes the segments by composite signal in an alternating, repeating sequence. The composite signal thus contains data from a plurality of senders.

However, many network environments that use time division multiplexing as described above tend to lose bandwidth due to internal delays within each node and transmission delays between nodes.

Accordingly, there is a need in the art for a method for compensating for internal delays within each node and transmission delays between nodes.

SUMMARY OF THE INVENTION

Various embodiments of the invention are directed to a method for synchronizing a real-time clock of a first node and a real-time clock of a second node with a real-time clock of a multiplexer. The method includes sending a real time clock of the multiplexer and the first number to the first node; setting the real-time clock of the first node equal to the real-time clock of the multiplexer; formation of the second number; sending the real-time clock of the multiplexer and the second number to the second node; and setting the real-time clock of the second node equal to the real-time clock of the multiplexer.

Various embodiments of the invention are also directed to a method for compensating for one or more transmission delays between a multiplexer, a first node and a second node. In one embodiment, the method includes calculating a transmission delay between the multiplexer and the first node using the equation ( RTC K + Delay K ) mod ( M · T slot ) = ( K-1 ) · T slot , where M denotes the number of time slots within the bandwidth of the medium configured to transfer data between the multiplexer, the first node and the second node, T slot denotes the duration of each time interval, K denotes the node address, mod denotes the take operation modulo, RTC K denotes the real time clock of the K-th node and delay k reads the accumulated transmission delay from the multiplexer to the Kth node; sending the real-time clock of the multiplexer, the first number and transmission delay to the first node; and setting the real-time clock of the first node equal to the real-time clock of the multiplexer plus transmission delay.

In yet another embodiment, the method includes synchronizing, by the first real-time clock of the multiplexer, both the real-time clock of the first node and the real-time clock of the second node; receiving data from the first node, calculating the transmission delay between the multiplexer and the first node using the equation ( RTC K + Delay K ) mod ( M · T slot ) = ( K · 1) · T slot , where M denotes the number of time intervals within the band transmitting the medium configured to transfer data between the multiplexer, the first node and the second node, T slot denotes the duration of each time interval, K indicates a node address, mod denotes a take operation modulo, RTC K denotes a real time clock of the Kth node, and Delay K refers to accumulated delay e transmission from the multiplexer to the K-th node; sending the second real-time clock of the multiplexer, the first number and transmission delay to the first node; and setting the real-time clock of the first node equal to the second real-time clock of the multiplexer plus transmission delay.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the above features of the present invention could be understood in detail, a more specific description of the invention, summarized above, is provided by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments of this invention, and therefore should not be construed as limiting its scope, since the invention may allow other equally effective embodiments.

FIG. 1 illustrates a network environment in accordance with one or more embodiments of the present invention.

FIG. 2 illustrates a flowchart of a method for synchronizing a real-time clock of each node within a network environment with a real-time clock of a multiplexer in accordance with one or more embodiments of the invention.

FIG. 3 illustrates a sync word in accordance with one or more embodiments of the invention.

FIG. 4 illustrates a flowchart of a method for compensating for transmission delay between a multiplexer and each node within a network environment in accordance with one or more embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a network environment 10 in accordance with one or more embodiments of the present invention. In one embodiment, the network environment 10 includes a multiplexer 20 in communication with a large number of nodes 100. FIG. 1 shows that the network environment 10 contains K nodes, and K can be any larger than one. Each node can be a sensor, a computer, a server, a wireless device, a personal digital assistant or any other device that can be used, being somehow connected respectively to a network environment 10. Network environment 10 can be a network of a seismological data acquisition system. The multiplexer 20 and the nodes 100 are connected to each other in a loop configuration. As such, the multiplexer 20, in most cases, may be referred to as a terminal device. All nodes 100 receive identical signals, and each node in the loop can modify one or more signals before transmitting them to the next node. Signals can be transmitted between nodes 100 and multiplexer 20 through any transmission medium, such as fiber optic cable or electrical wire.

Between adjacent nodes 100, there is a two-way communication. The signals that are transmitted from the multiplexer 20 to the nodes 100 can be transmitted via a command line 30, which can use a continuous, frame-based format. Signals that are transmitted from the multiplexer 100 to the nodes 20 can be transmitted via a data line 40, which can use time division multiplexing (TDM). Each node 100 may have a dedicated time slot for data transmission. Other embodiments, however, suggest that each node 100 may have more than one dedicated time slot for data transmission.

FIG. 2 illustrates a flowchart of a method 200 for synchronizing a real-time clock of each node within a network environment with 10 real-time clocks of a multiplexer 20 in accordance with one or more embodiments of the invention. At step 210, the multiplexer 20 generates a sync word. FIG. 3 illustrates a sync word 300 in accordance with one or more embodiments of the invention. Sync word 300 includes three fields: a real-time clock field, an address field, and a delay field. The real-time clock field is filled with the real-time clock of the multiplexer 20, which can be synchronized with the global real-time clock, for example, with the GPS real-time clock (global positioning system). As such, the real-time clock of the multiplexer 20 may be a real-time reference clock. The address field is filled in 1, which corresponds to the first node. The address field may be in any format widely known to those of ordinary skill in the art, for example, binary or decimal. The delay field is blank. At step 220, the multiplexer 20 sends a sync word to node 1. The sync word can be transmitted continuously through communication line 30. In one embodiment, the sync word may be transmitted at a fixed interval, which may be equal to or greater than the interval of the command frame.

At step 230, upon receiving the sync word, node 1 captures the real-time reference clock and sets the real-time reference clock as its real-time clock. Node 1 also captures the contents of the address field and sets the contents, that is, 1, as its network address. At step 240, the node 1 changes the sync word by incrementing the contents of the address field by one, that is 2, and translates the sync word to the next node in the loop. In this way, node 1 generates another number that should be used as the network address for the next node. The above steps are repeated until all nodes 100 within the network environment 10 have set the real-time reference clock as their real-time clock. That is, until the node K receives the sync word from the node K-1, fixes the real-time reference clock and sets the real-time reference clock as its real-time clock, and sets K as its network address (step 250).

Returning to step 210, as soon as the multiplexer 20 sends a sync word to node 1, the multiplexer 20 waits to receive data from nodes, including node 1. FIG. 4 illustrates a flowchart of a method 400 for compensating for transmission delay between a multiplexer and each node within a network environment 10 in accordance with one or more embodiments of the invention. Upon receipt of data from the node 1 (step 410), the multiplexer 20 measures the difference between the actual time of arrival of data from the node 1 to the multiplexer 20 and the actual time calculated using the following equation:

( RTC K + Delay K ) mod ( M · T slot ) = ( K-1) · T slot Equation (1)

where M indicates the number of time slots within the bandwidth, T slot indicates the duration of each time slot, K denotes the node address, RTC K denotes the real time clock of the Kth node; mod denotes the take operation modulo, and Delay K denotes the accumulated transmission delay from the multiplexer 20 to the Kth node (step 420). In the context of equation (1), multiplexer 20 can be considered as a node with K = 0, and multiplexer 20 uses a real-time reference clock in the form of RTC K. At step 430, the multiplexer 20 calculates Δt 1 , which is the transmission delay between the multiplexer 20 and the node 1, using the difference measured in step 420. The transmission delay Δt 1 may also include any delay that occurs in the node 1 associated with its internal data processing. In one embodiment, the transmission delay Δt 1 can be calculated as the difference measured in step 420 divided by 2.

At step 440, the multiplexer 20 generates a new sync word, which includes the real-time clock field, that is, filled with new real-time reference clock (for example, at the time when the sync word is generated), the address field filled in 1, and the delay field filled with the delay Δt 1 gear. At 450, the multiplexer 20 sends a new sync word to node 1.

At step 460, upon receiving the new sync word from the multiplexer 20, the node 1 sets the new real-time reference clock plus transmission delay Δt 1 as its new real-time clock. Node 1 also captures the contents of the address field and sets the contents, that is, 1, as its network address.

At step 470, node 1 measures the difference between the actual time of arrival of data from node 2 to node 1 and the actual time calculated using equation (1). At step 480, multiplexer 1 calculates Δt 2 , which is the transmission delay between node 1 and node 2, using the difference measured at step 470. At step 490, node 1 modifies the new sync word by incrementing the address field by one and setting the delay field = Δt 1 + Δt 2 , which can take into account any delay caused by the internal processing of node 1 and node 2. At step 495, node 1 sends a new sync word to node 2.

Processing continues until all nodes 100 within the network environment 10 set a new real-time reference clock plus its own corresponding accumulated transmission delay as its respective real-time clock. Once each node has set a new real-time reference clock plus its own corresponding accumulated transmission delay Δt as its real-time clock, each node can transmit data to the multiplexer 20 earlier, at its respective accumulated transmission delay Δt. For example, as soon as node 1 sets a new real-time reference clock plus transmission delay Δt 1 as its new real-time clock, node 1 can transmit data to multiplexer 20 earlier, by transmit delay Δt 1 . Similarly, as soon as node 2 sets a new real-time reference clock plus transmission delay Δt 1 + Δt 2 as its new real-time clock, node 2 can transmit data to multiplexer 20 earlier, to transmit delay Δt1 + Δt2. Thus, when the multiplexer 20 receives data from each node, the actual arrival time of data from each node will essentially be the same as the actual arrival time calculated using equation (1). Thus, various embodiments of the invention utilize transmission delay compensation to maximize bandwidth utilization.

Despite the fact that the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention can be devised without leaving its main scope, and its scope is defined by the claims, which follows.

Claims (29)

1. A method for synchronizing a real-time clock of a first node and a real-time clock of a second node with a real-time clock of a multiplexer, comprising the steps of:
send the real-time clock of the multiplexer and the first number to the first node;
set the real-time clock of the first node equal to the real-time clock of the multiplexer;
form a second number;
send the real-time clock of the multiplexer and the second number to the second node and
set the real-time clock of the second node equal to the real-time clock of the multiplexer.
2. The method according to claim 1, further comprising the step of setting the network address for the first node to the first number.
3. The method of claim 2, wherein setting the network address for the first node to the first number is performed by the first node.
4. The method according to claim 1, in which the real-time clock of the multiplexer and the first number are sent to the first node by the multiplexer.
5. The method according to claim 1, in which the real-time clock of the first node is set equal to the real-time clock of the multiplexer is performed by the first node.
6. The method according to claim 1, in which the formation of the second number is performed by the first node.
7. The method according to claim 1, wherein sending the real time clock of the multiplexer and the second number to the second node is performed by the first node.
8. The method according to claim 1, in which the real-time clock of the second node is set equal to the real-time clock of the multiplexer is performed by the second node.
9. The method according to claim 1, wherein sending the real-time clock of the multiplexer and the first number comprises the steps of:
form a sync word containing the real-time clock of the multiplexer and the first number; and
send a sync word to the first node.
10. The method according to claim 9, in which sending the real-time clock of the multiplexer and the second number to the second node comprises the steps of:
modify the sync word by replacing the first number with the second number and
send the modified sync word to the second node.
11. The method according to claim 1, in which the first node, the second node and the multiplexer are connected to each other in a loop configuration.
12. The method according to claim 1, in which data is transmitted between the first node, the second node and the multiplexer using time division multiplexing (TDM).
13. The method according to claim 1, further comprising the step of setting the network address for the second node to the second number.
14. The method according to claim 1, in which the formation of the second number comprises the step of incrementing the first number by one.
15. A method for compensating for one or more transmission delays between a multiplexer, a first node and a second node, comprising the steps of:
calculate the transmission delay between the multiplexer and the first node using the equation (RTC K + Delay K ) mod (M · T slot ) = (K-1) · T slot , where M denotes the number of time intervals within the transmission bandwidth of the medium configured for transmission data between the multiplexer, the first node and the second node, T slot denotes the duration of each time interval, K denotes the node address, mod denotes the take operation modulo, RTC K denotes the real-time clock of the Kth node and Delaw K denotes the accumulated transmission delay from the multiplexer to the Kth node;
send the real time clock of the multiplexer, the first number and the transmission delay to the first node and
set the real-time clock of the first node equal to the real-time clock of the multiplexer plus transmission delay.
16. The method according to clause 15, further comprising the step of sending data to the multiplexer earlier for a time determined by the transmission delay.
17. The method of claim 15, further comprising calculating a transmission delay between the first node and the second node using the equation.
18. The method according to 17, further comprising stages in which:
incrementing the first number by one to form a second number; and
send to the second node the real time clock of the multiplexer, the second number, the transmission delay between the multiplexer and the first node and the transmission delay between the first node and the second node.
19. The method of claim 18, further comprising setting the real time clock of the second node to the real time clock of the multiplexer, plus transmission delay between the multiplexer and the first node, plus transmission delay between the first node and the second node.
20. The method according to claim 19, further comprising sending data to the multiplexer earlier by the time determined by the transmission delay between the multiplexer and the first node plus the transmission delay between the first node and the second node.
21. The method according to clause 15, in which the transmission delay contains a delay caused by internal data processing within the first node.
22. The method according to clause 15, in which the calculation of the transmission delay between the multiplexer and the first node contains the step of measuring the difference between the time of arrival of data from the first node to the multiplexer and the arrival time calculated using the equation.
23. The method of claim 22, wherein calculating a transmission delay between the multiplexer and the first node further comprises calculating a transmission delay between the multiplexer and the first node using the measured difference.
24. The method of claim 15, further comprising setting a network address for the first node to the first number.
25. The method according to 17, in which the calculation of the transmission delay between the first node and the second node comprises the step of measuring the difference between the time of arrival of data from the second node to the first node and the arrival time calculated using the equation.
26. The method of claim 25, wherein calculating a transmission delay between the first node and the second node further comprises calculating a transmission delay between the first node and the second node using the measured difference.
27. A method for compensating for one or more transmission delays between a multiplexer, a first node and a second node, comprising the steps of:
synchronizing the first real-time clock of the multiplexer as the real-time clock of the first node and as the real-time clock of the second node;
receive data from the first node;
calculate the transmission delay between the multiplexer and the first node using the equation (RTC K + Delay K ) mod (M · T slot ) = (K-1) · T slot , where M denotes the number of time intervals within the transmission bandwidth of the medium configured for transmission data between the multiplexer, the first node and the second node, T slot denotes the duration of each time interval, K denotes the node address, mod denotes the take operation modulo, RTC K denotes the real-time clock of the Kth node and Delaw K denotes the accumulated transmission delay from the multiplexer to the Kth node;
send the second multiplexer real-time clock, the first number and transmission delay to the first node, and
set the real-time clock of the first node equal to the second real-time clock of the multiplexer, plus transmission delay;
28. The method according to item 27, further comprising the step of sending data to the multiplexer earlier for a time determined by the transmission delay.
29. The method according to item 27, in which the first real-time clock of the multiplexer is synchronized, both the real-time clock of the first node and the real-time clock of the second node, comprising the steps of:
send the first multiplexer real-time clock and the first number to the first node;
set the real-time clock of the first node in the form of the first real-time clock of a multiplexer;
form a second number;
send the first multiplexer real-time clock and the second number to the second node and
set the real-time clock of the second node equal to the first real-time clock of the multiplexer.
RU2006114170/09A 2005-04-26 2006-04-25 Method of compensating for internal delays within each node and transmission delays between nodes RU2414070C2 (en)

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US7447238B2 (en) 2008-11-04
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US20060239301A1 (en) 2006-10-26
GB0607476D0 (en) 2006-05-24
FR2887382A1 (en) 2006-12-22
RU2006114170A (en) 2007-11-20
GB2425695A (en) 2006-11-01

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